Surgical resection for cancer is becoming more minimally invasive with smaller incisions and less patient morbidity. However, this process switches the burden to the surgeon to remove all the disease with suboptimal visualization. This project proposes to develop a technique to employ pre- operative injection of ultra-sound contrast enhancement stationary microbubble and microshells to enable intraoperative detection of tumors even in cases with small skin incisions to allow surgeons to better identify and completely resect tumors and decease patient morbidty. Aims: To determine the optimal dose and lifetime of stationary microbubbles in a rabbit model as an ultrasound contrast agent in order to localize small breast tumors for surgical resection. To study the localization ability of a novel gas filled silica microshells compared to microbubbles as an ultrasound contrast agent and localization method for occult breast cancers using a rabbit model.